What frame rate do you want to be the main one? If 24p...23.98, then yes, you will have to convert all the 30fps to match using Compressor. And you'll need to set all the FRAME CONTROLS to BEST, and this means the conversions will take a LONG TIME. Note that they will not look exactly like the 24p footage, because it wasn't shot 24p, it was shot 30fps and converted. It'll be close, but it won't be exact....know that going in.

ALL the footage has to be converted to ProRes 422 before you edit...just in case you didn't know that.